Ultrasonic determination of laser manipulated changes in the elastic property of the intraocular lens

We propose using ultrasound to monitor the elastic property of the intraocular lens as manipulated by a femtosecond pulsed laser. To demonstrate this method, a lens and its zonules are extracted from a postmortem human eye globe. Free ends of the zonules are attached to an iris-like mechanical device that simulates accommodation muscles. The device and its attached lens are placed in a saline bath and scanned with an ultrasound microscope that uses a 50 MHz center frequency transducer with a 3 mm focus and f/# of 1.88. Thickness cross section images are produced for a lens in the relaxed state and at a radial deformation. Speckle within the lens is faint, but the lens capsule has a bright specular reflection. We can discern the composite elastic property of a lens by examining change in curvature of the anterior surface of the capsule for a given deformation. After measuring change in curvature, a loose grid of voids is created in the lens by a femtosecond pulsed laser. Change in curvature is then measured again. The lasered lens has greater change in curvature indicating greater tissue compliance. Results are consistent with what is expected considering a simple model of the lens system where capsule and media are parallel springs in series with zonules. This study indicates that ultrasound can monitor intraocular lens stiffness as manipulated by femtosecond laser microsurgery.